I need a cadillac seville sts 1998 4.3L & 32

Try Item #1 first it is the easiest.
Then Check the small water pump belt, it is not the serpentine belt.
The next step is to either check the Block with the following block tester available from NAPA
The part number is 700-1006
or change the thermostat dealer cost about 60.00 AUTOZONE about 40.00 You will need to purchase the Gasket with which ever you purchase from.

I had written a detailed note and the system dropped it. I hope this helps. coolant system drawing is available from:
http://media.photobucket.com/image/coolant%20system%20cadillac%20sts%201998/Parallax1/NSCoolingSystemCircuit.jpg

Check for coolant flow at the Purge line,this is a common problem on the Northstar.
There is a small diameter hose coming from near the top of the coolant tank,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.

I believe you have a 4.6L engine. These vehicles have known overheating issues. Chances are you have a engine mechanical problem. If you do not have any coolant leaks and the thermostat is working ok, you really need to take it to someone who has worked on that engine before.